The present invention relates to a method and a system for maintaining tightness between two coaxial pipes transferring fluid under very high pressure and rotatable relative to each other around a common axis so as to enable, for example, a transfer of fluid under pressure between two parts of a machine which rotate relative to each other.
The method and system of the invention is particularly suitable for this function when the rotation between two parts of the machine is slow and alternating and has a small amplitude, with the fluid pressure being very high and the required service life being very long.
So-called swivel joints maintaining tightness between two coaxial pipes rotating alternately to each other are well known, with the swivel joints using a elastic material packings associated with cylindrical or flat and annular bearing surfaces against which they are applied, especially by the fluid pressure. Rotation of one of the two co-axial pipes relative to each other can only be obtained by the sliding of the packing and its bearing surface.
When the pressure of the fluid to be transferred is very high, the elastic material packings are strongly pressed against their bearing surface and sliding causes rapid wear of the elastic material packings. Additionally, when the fluid pressure is very high, the sealing lips of the elastic material are subjected to a severe shearing stress.
Currently, materials for the manufacturing of packings which have the necessary flexibility for perfect mating with cooperating bearing surfaces generally do not have a sufficient shear strength and the lips of the packing may be destroyed by tearing, especially upon reversing a direction of rotation of the system.
Therefore, the present invention proposes a system wherein the contacting components are not driven with any relative rotational motion and, without damage, may be pressed against each other as strongly as necessary, to form an efficient barrier regardless the pressure of the fluid.
Systems of the aforementioned type are disclosed in, for example, U.S. Pat. Nos. 3,944,263, 2,253,932 and 3,689,082 along with French patents A-2,227,784, A-1,572,520, A-1,585,213, and A-1,310,665, with these patents relating to static or non-rotating joints and swivel joints.
The aim underlying the present invention essentially resides in providing a system for maintaining tightness between co-axial pipes rotating relative to each other and which is capable of confining a fluid under very high pressure, with the system being sturdy and wear resistant so as to enable a long service life.
Advantageously, the present invention may be used as a substitute for the prior art swivel joints used on fluid transfer systems such as, for example, transfer systems between marine structures and a ship such as, for example, an oil tanker, especially when the two structures are connected by an arm and are free to rotate relative to each other.
According to advantageous features of the present invention, a system is proposed for maintaining tightness between two parts rotatable relative to each other, wherein at least two sealing units are provided, with each of these sealing units having at least two possible states, namely, one state ensuring tightness between the parts and the second state not ensuring tightness. Each of these sealing units is deformable and the drive means may be provided for intermittently actuating each of the sealing units.
In accordance with the present invention, at least one of the sealing units, not always the same sealing unit is permanently in the first state and sealing may be accomplished by rotating the pipes relatively to each other around a common axis.
At least one of the sealing units may comprise a sleeve adapted to be subjected to elastic torsional deformation along an axis thereof, tightly connected at one end to one of the pipes and including at the other end thereof a flange provided with temporary connection means to the other pipe.
According to the invention, the sleeve may comprise at least one rigid ferrule connected, over a portion of the length thereof, to one of the two pipes through a first ferrule made of elastically deformable material, with one of the two cylindrical lateral faces adhering to the pipe and the other to the rigid ferrule, and, over another portion of a length of the sleeve, to the flange provided with the temporary connection means through a second elastically deformable ferrule, with one of the two cylindrical lateral faces adhering to the flange and the other to the rigid ferrule.
It is possible in accordance with the present invention for the sleeve to include a stack of flat elastically deformable rings, with a flat ring located at one of the ends of the sleeve adhering to a flange integral with one of the two pressure fluid transfer pipes, and a flat ring located at the other end of the sleeve adhering to the flange provided with the temporary connection means and the other pressure fluid transfer pipe.
In accordance with further features of the present invention, the sleeve may be a flexible elastically deformable tube and, if necessary reinforced by a tensile resistant wire armor, with one of the ends of the tube including a flange integral with one of the two pressure fluid transfer pipes, and the other end of the tube including another flange provided with temporary connection means to the other pressure fluid transfer pipe.
According to the invention, the temporary connection means may comprise an elastically deformable ring placed around the pipe to be connected, with the ring being disposed in a groove provided in the end of the flange of the sleeve and one of the lateral walls of which is movable and actuated by an annular hydraulic jack.
The shape of the ring is changed from an initial shape when temporarily subjected to compression stress along its axis by the annular hydraulic jack, and transmits the compression stresses radially around the pipe to simultaneously insure tightness between the sleeve and the pipe and to provide a rotational driving of the end flange of the sleeve by the fluid transfer pipe.
In accordance with still further features of the invention, the temporary connection means may comprise a tight and elastic membrane integral with the end flange of the sleeve adapted to be subjected to elastic torsional deformation, with which it defines a variable geometry annular chamber concentric with the pressure fluid transfer pipe, the membrane being able to take, depending on whether the chamber which it defines is fed with pressure fluid or not, a first position where, inflated, it is strongly applied against the pipe and ensures tightness between the sleeve and the pipe and provides a rotational driving, by friction of the end flange of the sleeve by the aforementioned pipe and a second position where, deflated, it is returned by its own elastic stiffness against the flange in its initial shape at rest, and is no longer in contact with the aforementioned pipe.
Advantageously, this tight and elastic membrane may be an elastomeric tube fixed at both ends unto the end flange of the sleeve liable to elastic deformation, with which it defines a pressurizable annular chamber and whose compressive strength and elastic deformability are ensured by an internal armor made of braided wires, the wires forming between themselves a suitable angle, close to 20.degree., so that under the pressurization action of the chamber, the diameter of the tube may be increased by modification of the angle formed between themselves by the braided wires, and return to its initial size when the pressure fluid feed is stopped, by elastic return of the elastomer between the braided wires.
Additionally, according to further features of the invention, the temporary connection means may comprise a collar integral with the fluid transfer pipe to be connected and fixed in a groove provided in the end flange of the sleeve adapted to be subjected to elastic torsional deformation, with the side walls of the groove being composed of the body and the ram of an annular hydraulic jack. In this case, and with the forced fed fluid of the cylinder of the hydraulic jack causes the side walls to be brought closer to one another and to strongly nip the collar so as the ensure, tightness between the sleeve and the collar and the rotation by friction of the end flange of the sleeve through the aforementioned pipe.
Advantageously, the annular hydraulic jack which actuates the mobile side wall of the groove provided in the end flange of the elastic sleeve comprises a jack body and a ram which are co-axial and are interconnected on either side of the pressurizable annular chamber which they confine, by two ferrules of elastically deformable material. The side faces of the ferrules adhere to the jack body and the ram, so that the axial motion of the ram in one direction, under the effect of the pressure of the fluid contained in the annular chamber is tolerated by the shear deformation of the flexible material of the ferrules and the motion in the opposite direction can be obtained, when pressure rise in the annular chambers is interrupted, by the elastic stiffness of the flexible material of the ferrules which tends to recover to its initial shape.
According to the invention, the drive which intermittently actuates each of the two units providing tightness between the two pipes may be connected to the rotation of these two pipes in relation to each other through a cam integral with one of the two aforementioned pipes and in a position detector connected through the cam and fixed to the other pipe, the detector starting the operation of the connection means fitted on the sealing units.
Advantageously, the position detector may be a three position fluid slide valve to which the four pipes are connected and the cam with which is associated a slide operation feeler may have a three level contour. Two of the pipes connect each of the valves to each of the temporary connection means provided on the intermittently actuated sealing units. The third pipe connects the valve to a pressure fluid generator associated with a pressure accumulator, and the fourth pipe connects the valve to an atmospheric receiver tank out of which the aforementioned generator draws the fluid which it pressurizes. The three positions of the valve then correspond to the tripping sequences of the sealing units during which, successively, only one of the two aforementioned units is in operation, then both of them, then only the second etc., each of these sequences corresponding to one of the three levels of the cam.
As an alternative, with a view towards supplying the temporary connection means with pressure fluid, a pipe may connect the slide valve to the system comprising the two-coaxial fluid transfer pipes rotating in relation to each other so that the energy of the fluid to be confined can be used directly to operate the connection means.
To this end, a pressure booster comprising a staggered piston sliding in the tight body with two-coaxial bores mays be provided on the pressure fluid supply system of the temporary connection means.